The occlusion (stenosis) of small blood vessels that occurs, for example, as a result of the accumulation of atherosclerotic plaques, is a major cause of morbidity and mortality in the western world. While the detection of such occlusions may be readily performed by several techniques including angiography and ultrasonic echocardiography, the accurate measurement of both the degree of vascular stenosis and hence of vascular dysfunction, without resorting to highly invasive techniques, is much more difficult to achieve.
A number of techniques for quantifying vascular occlusion are known in the art. While some of these methods provide reliable quantitative data, they are generally highly invasive in nature. Examples of such methods include the technique described in U.S. Pat. No. 5,752,522 (Murphy), in which the cross-sectional dimensions of a blood vessel are determined by inflation of a balloon catheter within the blood vessel lumen, until the balloon diameter matches the lumen diameter. A further method is the measurement of myocardial fractional flow reserve, in which an index representing the degree of coronary artery stenosis is calculated from measurements of mean distal intracoronary pressure and of mean arterial pressure (Pijls et al. New Engl. J. Med. 334: 1703-1708, 1996).
Both of the abovementioned prior art methods for measuring the degree of vascular stenosis are technically demanding in that they require catheters to be positioned at very specific locations in relation to the site of the stenosis, as well as the use of vasodilatory drugs.
It has now been surprisingly found, and this is an object of the invention, that it is possible to obtain an accurate measure of the degree of constriction or occlusion of a conduit from simultaneous measurement of fluid pressure and flow through said conduit, over a period of time. Furthermore, these simultaneous measurements may be used to determine the elastic properties of conduits. Such determinations are of clinical importance, as they permit assessment of the extent of, for example, atherosclerotic disease in blood vessels. In this system, the relationship between pressure and flow is not a simple linear one. Rather, when plotted graphically, the resulting curve is in the form of a closed loop, whose area may be measured and used to determine the degree of occlusion of the conduit. Furthermore, the slope and y-axis intercept of the line joining the two inflection points situated at the extremities of the major axis of the loop, may also be used to determine the same variable, that is, the degree of occlusion of the conduit, as well as its elasticity.
It has further been unexpectedly found that a quantitative measure of the elastic properties of a conduit may be derived from the polynomial equation that describes the relationship between the above-described area enclosed by the pressure-flow relationship and the degree of occlusion of a conduit of the same material.
It is a purpose of this invention to provide a method for the accurate quantification of the degree of partial constriction of blood vessels and other types of tube or conduit.
It is another purpose of this invention to provide a method for accurately quantifying the degree of partial constriction that uses fluid pressure and flow data obtained by minimally invasive methods.
It is yet another purpose of this invention to provide such a method that calculates the degree of partial constriction in a manner that is independent of the apparatus or technique used to obtain the pressure and flow data.
It is a further purpose of this invention to provide a method for calculating the degree of partial occlusion of a conduit that is independent of the distance between the site of said partial occlusion and the site of the pressure and flow measurements, and without the requirement for vasodilatory or other drugs.
It is a further purpose of this invention to provide apparatus for determining the degree of partial occlusion of a conduit.
It is a further purpose of this invention to provide a method for assessing the elastic properties of a conduit, using fluid pressure and flow rate data.
It is a further purpose of this invention to provide apparatus for determining the elastic properties of a conduit.
Other objects and advantages of the invention will become apparent as the description proceeds.